Apparatus and methods for testing acoustic probes and systems

ABSTRACT

Methods and apparatus are provided for testing an acoustic device that has multiple transducing elements adapted for conversion between acoustic and electrical signals. An electrical transmission signal is generated. The electrical transmission signal is transmitted to a selected transducing element. An electrical received signal is received from the acoustic device. A reference signal is generated. A capacitance associated with the selected transducing element is determined from the reference signal. Operational characteristics of the selected transducing element are diagnosed from the determined capacitance and the electrical received signal.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is related to the following concurrently filed,commonly assigned U.S. patent applications, the entire disclosure ofeach of which is incorporated herein by reference in its entirety:“APPARATUS AND METHODS FOR TESTING ACOUSTIC SYSTEMS,” by James M.Gessert et al. and “APPARATUS AND METHODS FOR INTERFACING ACOUSTICTESTING APPARATUS WITH ACOUSTIC PROBES AND SYSTEMS,” by James M. Gessertet al. The above applications are, respectively, Ser. Nos. 10/426,156and 10/426,066, both filed Apr. 28, 2003.

BACKGROUND OF THE INVENTION

This application relates generally to acoustic probes and systems. Morespecifically, this application relates to apparatus and methods fortesting acoustic probes and systems.

Acoustic imaging techniques have been found to be extremely valuable ina variety of applications. While medical applications in the form ofultrasound imaging are perhaps the most well known, acoustic techniquesare more generally used at a variety of different acoustic frequenciesfor imaging a variety of different phenomena. For example, acousticimaging techniques may be used for the identification of structuraldefects, for detection of impurities, as well as for the detection oftissue abnormalities in living bodies. All such techniques relygenerally on the fact that different structures, whether they becancerous lesions in a body or defects in an airplane wing, havedifferent acoustic impedances. When acoustic radiation is incident on anacoustic interface, such as where the acoustic impedance changesdiscontinuously, it may be scattered in ways that permitcharacterization of the interface. Radiation reflected by the interfaceis most commonly detected in such applications, but transmittedradiation is also used for such analysis in some applications.

Transmission of the acoustic radiation towards a target and receipt ofthe scattered radiation may be performed and/or coordinated with amodern acoustic imaging system. Many modern such systems are based onmultiple-element array transducers that may have linear, curved-linear,phased-array, or similar characteristics. These transducers may, forexample, form part of an acoustic probe. In some instances, the imagingsystems are equipped with internal self-diagnostic capabilities thatallow limited verification of system operation, but do not generallyprovide effective diagnosis of the transmission and receiving elementsthemselves. Degradation in performance of these elements is often subtleand occurs as a result of extended transducer use and/or through userabuse. Acoustic imaging devices therefore often lack any directquantitative method for evaluating either system or probe performance.Users and technical support personnel thus sometimes use phantoms thatmimic characteristics of the object under study to provide a qualitativemethod for evaluating image quality and to perform a differentialdiagnosis between the system and the transducer array, but thistechnique is widely recognized to be of limited utility.

There is, therefore, a general need in the art for apparatus and methodsfor testing acoustic probes and systems.

BRIEF SUMMARY OF THE INVENTION

In embodiments of the invention, a method is provided for testing anacoustic device that has a plurality of transducing elements adapted forconversion between acoustic and electrical signals. An electricaltransmission signal is generated. The electrical transmission signal istransmitted to a selected transducing element. An electrical receivedsignal is received from the acoustic device. A reference signal isgenerated. A capacitance associated with the selected transducingelement is determined from the reference signal. Operationalcharacteristics of the selected transducing element are diagnosed fromthe determined capacitance and the electrical received signal.

The electrical received signal may correspond to an acoustic signalconverted from the electrical transmission signal and reflected from atarget. The electrical transmission signal may comprise a voltage pulse.In one embodiment, transmitting the electrical transmission signalcomprises routing the electrical transmission signal through a relayelement configured for selective routing from a channel to a pluralityof channels. The electrical transmission signal may be further routedthrough an adapter having a multichannel switch.

The reference signal may comprise a linear voltage ramp. In oneembodiment, the selected transducing element comprises a piezoelectriccrystal and the reference signal is generated with a frequency less thana resonant frequency of the piezoelectric crystal. For example, thereference signal may have a frequency less than 100 kHz or may have afrequency less than 10 kHz. In another embodiment, the resonantfrequency of the piezoelectric crystal is between 2 and 10 MHz and thereference signal has a frequency between 0.5 and 1.5 MHz.

The capacitance information provides various diagnostic capabilities.For example, in one embodiment, the selected transducing elementcomprises a cable connection and the capacitance derives at least inpart from a cable capacitance of the cable connection. Diagnosing theoperational characteristics comprises determining that the capacitancearising from the cable capacitance is a fraction of an expected value.In another embodiment, diagnosis comprises determining that an amplitudeof the electrical received signal is substantially zero and determiningwhether the capacitance is consistent with an expected value.

These methods may be embodied on apparatus for testing the acousticdevice. A transmitter may be provided to generate the electricaltransmission signal. A relay element may be provided to route theelectrical transmission signal to the selected transducing element. Areceiver may be provided to receive the electrical received signal fromthe acoustic device. A waveform generator may be provided to generatethe reference signal with which the capacitance associated with theselected transducing element is determined. In addition, in someembodiments, a computational unit may be provided to diagnose theoperation characteristics of the selected transducing element from thedetermined capacitance and the electrical received signal. In otherembodiments, an adapter may be provided to interface between the relayelement and the transducing elements, the adapter having a multichannelswitch.

The methods of the invention may also be embodied in a computer-readablestorage medium having a computer-readable program embodied therein fordirecting operation of the apparatus. The computer-readable programincludes instructions for operating the apparatus to test an acousticdevice in accordance with the embodiments described above.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings wherein like reference numerals are usedthroughout the several drawings to refer to similar components.

FIG. 1 is a block-diagram representation of an arrangement used fortesting an acoustic probe in accordance with embodiments of theinvention;

FIG. 2 is a schematic representation of a probe geometry that may betested with embodiments of the invention;

FIG. 3 is a block-diagram representation of a computational unit onwhich methods of the invention may be embodied;

FIG. 4 is a circuit diagram illustrating a receiver unit used inembodiments of the invention;

FIG. 5A is a circuit diagram illustrating a capacitance circuit used inembodiments of the invention;

FIG. 5B illustrates a ramp profile for a pulse used by the waveformgenerator of FIG. 5A;

FIGS. 6A and 6B illustrate series and parallel tuning arrangements of anacoustic probe;

FIG. 7 is a flow diagram illustrating methods for testing an acousticprobe in accordance with embodiments of the invention;

FIG. 8 is a schematic representation of an acoustic element that may bediagnosed in accordance with embodiments of the invention;

FIG. 9 is a block-diagram representation of an acoustic system that maybe tested in accordance with embodiments of the invention;

FIG. 10 is a block-diagram representation of an arrangement used fortesting an acoustic system in accordance with embodiments of theinvention;

FIGS. 11A and 11B are flow diagrams illustrating methods for testing anacoustic system in accordance with embodiments of the invention;

FIG. 12 is a schematic illustration of an adapter used by testarrangements in embodiments of the invention;

FIGS. 13A and 13B are circuit-diagram illustrations of switchconfigurations that may be comprised by the adapter illustrated in FIG.12;

FIG. 14 is a flow diagram illustrating methods for testing an acousticprobe or acoustic system in accordance with embodiments of theinvention;

FIG. 15 is a block-diagram illustration of an arrangement used fortesting a multiplexing acoustic probe in accordance with embodiments ofthe invention; and

FIG. 16 is a flow diagram illustrating methods for testing amultiplexing acoustic probe in accordance with embodiments of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

1. Introduction

Embodiments of the invention provide apparatus and methods for testingacoustic probes and systems. Such acoustic probes and systems aresometimes referred to herein collectively as “acoustic devices.” Whilemuch of the discussion below specifically discusses apparatus andmethods that are suitable for testing ultrasonic probes and systems,this is intended merely for exemplary purposes and the invention is notintended to be limited by the operational frequency characteristics usedby the tested probe or system. As illustrated in further detail below,each of the acoustic probes and systems that may be tested withembodiments of the invention includes a plurality of “transducerelements,” which refers to elements adapted to transmit acousticradiation and/or to receive acoustic radiation. While such elements arereferred to generically herein as “transducer elements,” reference issometimes also made herein to “receiver elements” and to “transmitterelements” to distinguish them on the basis of their functions. Methodsof the invention diagnose operation of the probe or system throughsequential activation of the component transducer elements. In the caseof a probe, such sequential activation may be initiated externally whilein the case of a system, such sequential activation may use a naturaloperational cycling of the system.

For example, testing of an acoustic probe in embodiments of theinvention may be performed by placing the probe in a test fixture in anacoustically conductive medium with a specular reflector provided at asubstantially uniform distance to all of the transducer elements.Conveniently, the acoustically conductive medium may comprise water inan embodiment. The array of transducing elements comprised by the probeare then activated sequentially so that acoustic radiation istransmitted through the acoustically conductive medium towards thespecular reflector. While the sequential activation may take place byactivating transducing elements individually, this is not a requirement,and sequential activation may alternatively be performed simultaneouslywith a subset plurality of the transducing elements. Reflections fromthe specular reflector are digitized, and perhaps also amplified, forevaluation of the activated transducing elements. Selective activationof the transducing elements may be coordinated by a relay matrix thatselectively establishes operational connections with the transducingelements.

Testing of an acoustic system in embodiments of the invention may beperformed with a similar relay matrix for selectively establishingoperational connections with channels comprised by the acoustic system.Connections may be established sequentially with the channels, eitherindividually or in groups. This permits evaluation of a transmittercircuit comprised by the acoustic system as it is connected through eachchannel. In addition, scattering operations may be simulatedelectronically for each channel by transmission of an echo signalthrough the sequential connections. Operation of a receiver circuitcomprised by the acoustic system may thus be evaluated throughevaluation of image data produced by the acoustic system in response tothe simulated scattering operations.

2. Acoustic-Probe Testing

An overview of embodiments of the invention suitable for testing anacoustic probe is provided with the structural diagram of FIG. 1.Testing of a probe may use signals generated by a transmitter 124. Inone embodiment, such signals are generated to provide a broadband pulsethat excites all of the transducer elements comprised by the probe in asubstantially similar manner. For example, the signal may comprise avoltage pulse. In a particular embodiment suitable for testing manycommercially available acoustic probes, the signal comprises anapproximately 40-ns pulse at a magnitude of about 75 V, which provides

25 MHz bandwidth.

The signal generated by the transmitter 124 is routed to a selected oneor subset group of the transducing elements for conversion into anacoustic signal by a relay matrix 108 and an adapter 104. In cases wherea signal is routed simultaneously to a subset group of the transducingelements, the subset group may correspond to a group of neighboringtransducing elements. The relay matrix 108 comprises a bidirectionalswitching array capable of establishing the desired connections. It isgenerally desirable for electrical characteristics of the relay matrixnot to impact the evaluation of the transducing elements. Accordingly,an array of miniature relays may be preferred in some embodiments oversemiconductor-based switching integrated circuitry to limit capacitiveand resistive loads. The relays may be arranged in groups to limit thenumber of traces that may be active at any given time. In addition, aregular circuit topology may be used to keep the electrical loadsubstantially constant. In one embodiment, a correction factordetermined uniquely for each element may be used to further reducemeasurement errors that may be associated with electrical loadingassociated with the relay matrix.

The relay matrix 108 may be considered to perform a mapping from onechannel that corresponds to the transmitter 124 to a plurality ofchannels that are in communication with the adapter 104. The adapter 104itself may be configured in accordance with characteristics of the probeto be tested, allowing connectivity between the relay matrix 108 andprobes from a variety of different manufacturers. In some embodiments,the adapter 104 is configured to provide a 1:1 mapping from transducingelements of the probe to channels of the relay matrix 108. Thus, forexample, if the probe has 192 transducing elements, the adapter 104 maymap each of 192 channels from the relay matrix 108 to one of thetransducing elements. In other embodiments described in further detailbelow, the adapter 104 is configured to provide different schemes formapping channels from the relay matrix 108 to transducing elements ofthe probe.

During testing, the probe may be secured within a holder 120 adapted tomaintain a fixed distance of each of the transducing elements from theacoustically reflective target 116, the assembly of holder 112 andtarget 116 being denoted generically with reference numeral 120. Theholder 120 may also be equipped with adjustment capabilities,permitting, for example, the angular orientation of the probe to beadjusted as desired. In some instances, the reflective target 116 maycomprise a flat surface, but in other instances, the shape of the target116 may mimic a shape of the probe to compensate for positions of thetransducing elements according to the probe shape. This is illustratedis FIG. 2 for a probe 200 that has a curved tip. The curvature of theprobe tip is compensated for by a curvature of the reflective target116′, the curved portion of the probe tip and the reflective target 116′having a common center of curvature 204.

The transducing elements of the probe act to convert the signalgenerated by the transmitter 124 into an acoustic signal that isreflected from the target 116. The reflected acoustic signal is receivedby one of the transducing elements of the probe and converted into anelectrical signal, which is routed back through the adapter 104 andrelay matrix 108. The converted signal is received by a receiver 136,which may include an attenuator to reduce pulse amplitude, andtransmitted to an analog-to-digital converter 140. In one embodiment thereceiver has an output between 0 and 1 V and has a 1-dB bandwidth ofabout 10 MHz. The analog-to-digital converter 140 may advantageously beadapted to accommodate high sample rates in order to accurately samplethe acoustic signals. In one embodiment, the analog-to-digital converter140 is adapted to accommodate sample rates of at least 100 MHz. At sucha rate, at least ten samples may be retrieved per cycle on a 10-MHzprobe. In some instances, the analog-to-digital converter 140 mayadditionally include a video-frame-capture capability to permitcapturing of an ultrasonic image for further use as described below. Theoutput of the analog-to-digital converter 140 is routed to acomputational unit 132 for analysis and/or display, in some instancesthrough an intermediary first-in-first-out (“FIFO”) memory 144 toaccount for the high speed of the analog-to-digital converter 140.

The computational unit 132 may comprise any device having processingcapability sufficient to analyze data received from theanalog-to-digital converter 140 in accordance with embodiments of theinvention. For example, the computational unit 132 may comprise apersonal computer, a mainframe, or a laptop, whose mobility makes itespecially convenient. The dashed lines in FIG. 1 illustrate that, inaddition to receiving data for analysis, the computational unit 132 maybe configured to control each of the components comprised by the testingapparatus.

FIG. 3 provides a schematic illustration of a structural arrangementthat may be used to implement the computational unit 132. FIG. 3 broadlyillustrates how individual elements of the computational unit 132 may beimplemented in a separated or more integrated manner. The computationalunit 132 is shown comprised of hardware elements that are electricallycoupled via bus 326, including a processor 302, an input device 304, anoutput device 306, a storage device 308, a computer-readable storagemedia reader 310 a, a communications system 314, a processingacceleration unit 316 such as a DSP or special-purpose processor, and amemory 318. The computer-readable storage media reader 310 a is furtherconnected to a computer-readable storage medium 310 b, the combinationcomprehensively representing remote, local, fixed, and/or removablestorage devices plus storage media for temporarily and/or morepermanently containing computer-readable information. The communicationssystem 314 may comprise a wired, wireless, modem, and/or other type ofinterfacing connection and permits data to be exchanged with externaldevices as desired.

The computational unit 132 also comprises software elements, shown asbeing currently located within working memory 320, including anoperating system 324 and other code 322, such as a program designed toimplement methods of the invention. It will be apparent to those skilledin the art that substantial variations may be made in accordance withspecific requirements. For example, customized hardware might also beused and/or particular elements might be implemented in hardware,software (including portable software, such as applets), or both.Further, connection to other computing devices such as networkinput/output devices may be employed. Connections between thecomputational unit 132 and the various components of the testingapparatus may use any suitable connection, such as a parallel-portconnection, a universal-serial-bus (“USB”) connection, and the like.

An explicit example of a circuit structure that may be used for thereceiver 136 in one embodiment is illustrated in FIG. 4. In thisexample, the receiver 136 comprises an attenuator 412 to reduce pulseamplitude and provide input protection for the receiver as well as avariable-gain amplifier 404. A typical range for the variable-gainamplifier 404 may be −20 to +60 dB, although a narrower range, such as+6to +30 dB may be adequate for testing many commercially availableprobes. The variable-gain amplifier 404 may be controlled by thecomputational unit 132, with a digital-to-analog converter 408 beingused to convert instructions from the computational unit 132. In oneembodiment, the variable-gain amplifier 404 is configured such that alinear change in voltage corresponds to a logarithmic change in gain.

The configuration described in connection with FIGS. 1–4 is sufficientin many instances to permit a diagnosis of transducing-element operationin acoustic probes. For example, receipt of a signal during cyclingthrough the transducer elements when correlated with a time ofinterrogation indicates that a specific element is functioningcorrectly, while failure to receive a signal indicates that that elementis not functioning correctly. In several embodiments, this informationis augmented by analyzing the capacitance of elements in the system toprovide additional useful diagnostic information. The capacitanceanalyses make use of a waveform-generator 128, also shown in FIG. 1 asbeing under the control of the computational unit 132.

A circuit structure of the waveform generator 128 is illustrated for aparticular embodiment in FIG. 5A. A waveform is generated digitally by acounter 504, with the waveform having a variation in voltage ΔV overtime Δt, thereby defining a capacitance

$C \equiv {\frac{i}{( {\Delta\;{V/\Delta}\; t} )}.}$The waveform is converted with a digital-to-analog converter 508 andamplified with an amplifier 512. The waveform is transmitted onto thechannel 524 that feeds to the relay matrix with a source resistance 520used to drive the probe and with an instrumentation amplifier 516. Asuitable value for the source resistance 520 in a particular embodimentis approximately 10 kΩ. While the invention is not limited to a specificshape for the capacitance-defining waveform, it may conveniently takethe form of a linear ramp function 532 such as shown in FIG. 5B, therebyproviding a constant capacitance. Merely by way of example, the voltageincrease of the waveform could be ΔV=4.096 V over a time period ofΔt=409.6 μs, thereby providing a capacitance of C=i/10⁴ F.

For the simplest probe structure, the capacitance of each of thetransducing elements may thus be determined during interrogation of thatelement by generating the waveform and measuring the resulting currenti. In some instances, this method may be complicated by a probestructure that provides an additional significant source of capacitance.In particular, each transducing element may comprise a piezoelectriccrystal used to perform electrical-acoustic conversions. The probe maysupply energy to each such piezoelectric crystal with a coaxial cablethat has an intrinsically high capacitance. Accordingly, such probemanufacturers often use a tuning circuit to tune out the capacitance ofthe coaxial cable and thereby permit effective energy coupling into thepiezoelectric crystal. Any suitable tuning circuit known to those ofskill in the art may be used, such as with a standard second-order tunedcircuit. The tuning circuit typically comprises an inductive element,which may be provided in series or in parallel with the piezoelectriccrystal. Methods of the invention may account for the specificconfiguration of the tuning circuit in different embodiments.

The electrical structure of a series-inductor tuned probe 604 isillustrated in FIG. 6A. Energy is coupled into the piezoelectric crystal610 comprised by each transducing element with a coaxial cable 608. Thecircuit for tuning out the capacitance of the coaxial cable 608comprises an inductive element 612 provided in series with thepiezoelectric crystal 610, and may also include a resistive element (notshown), usually provided in parallel with the piezoelectric crystal 610.Testing of such a series-inductor tuned probe 604 may thus be performedin a manner similar to that used for an untuned probe. In particular,the waveform generator 128 may provide a low-frequency waveform, i.e.such as on the order of less than 10 kHz or less than 100 kHz dependingon the embodiment, and the resulting current i measured. The capacitanceis then determined from the ratio of the current i to the time rate ofchange of voltage in the waveform.

Use of such a low-frequency waveform may be less effective for aparallel-inductor tuned probe 606 such as illustrated in FIG. 6B. Inthis instance, the tuning circuit comprises an inductive element 612′provided in parallel with the piezoelectric crystal 610′, and may alsoinclude a resistive element (not shown), usually also provided inparallel with the piezoelectric crystal 610′. With such an arrangement,a low-frequency waveform on the order of less than 100 kHz results in asmall inductive reactance. Accordingly, in some embodiments, a higherfrequency is used for the waveform. This frequency is chosen to beoutside the active range of the piezoelectric crystal to avoidspuriously interfering with the operation of the probe, such as below aresonant-frequency range of the piezoelectric crystal. For example, ifthe piezoelectric crystal has a resonant frequency in the range of 2–10MHz, which is common for ultrasonic applications, the frequency of thewaveform may be in the range of 0.5–1.5 MHz, such as at approximately1.25 MHz.

Methods that may be used by the arrangements described in connectionwith FIGS. 1–6B to test the operation of a probe are thus summarizedwith the flow diagram of FIG. 7. While the flow diagram is provided witha specific ordering, it will be appreciated that there is no requirementthat this ordering be followed. In alternative embodiments, functionsmay be performed simultaneously even if they are shown separately inFIG. 7, and may be performed in a different order than the specificexample shown in FIG. 7. At block 704, the method begins by selecting afirst transducer of the probe to be interrogated. The selectedtransducer may be selected according to a routing defined by the relaymatrix 108 and coupled operationally to the selected transducingelements through the adapter 104. This routing is used to transmit anelectrical transmission signal generated at block 708 and a referencewaveform generated at block 712 to the selected transducing element. Thetransducing element acts to convert the electrical transmission signalto an acoustic transmission signal at block 716. After the acoustictransmission signal is reflected from the target at block 720 andreceived at block 724, it is converted to an electrical received signal.

This same procedure is performed sequentially for each of thetransducing elements. This is indicated at blocks 732 and 736 where acheck is made whether all transducing elements have been interrogated,and the next transducing element being selected if they have not been.Once interrogation of all the transducing elements comprised by theprobe has been completed, the collected data are analyzed to diagnosewhether any of the transducing elements is failing to operate withinnormal parameters. A comparison of the amplitudes of the receivedsignals at block 740 provides a broad measure of whether there is adefect associated with any of the transducing elements; this is usuallyindicated by lack of a received signal, which identifies a correspondingdefect, although a substantially reduced amplitude may also provide asimilar indication.

More detailed diagnostic information is provided by a comparison ofcapacitance associated with the interrogation of each of the transducingelements with the reference waveform, as performed at block 744. Thediagnostic value of such capacitance determinations may be illustratedwith some examples, which are provided herein merely for illustrativepurposes and are not intended to limit the scope of the invention; otherdiagnostic capabilities resulting from the capacitance determinationswill be evident to those of skill in the art after reading thisdescription.

A first example may be understood with reference to FIG. 8, whichprovides a schematic illustration of a structure that may be used forone of the transducing elements 800. The transducing element comprises abacking 816 over which the piezoelectric crystal 812 is provided. Anacoustic lens 804 provided over the piezoelectric crystal 812 provideselectrical isolation of the piezoelectric crystal 812 and acousticimpedance matching. A defect in the operation of the transducing element800 may result from different types of conditions that may bediscriminated by the capacitance determinations. For example, the defectmay result from delamination of the acoustic lens 804 from thepiezoelectric crystal 812. This condition is manifested by lack of anelectrical received signal concomitant with substantial matching of thecapacitance of the particular transducing element with the capacitanceof fully functioning transducing elements. The defect may alternativelyresult from cracking or other damage to the piezoelectric crystal 812.This condition is manifested by lack of an electrical received signalconcomitant with a failure of the capacitance of the particulartransducing element to match the capacitance of fully functioningtransducing elements.

In another example, the capacitance determinations may be used toidentify defects associated with the coaxial cables used to coupleenergy to the respective piezoelectric crystals. The capacitancedetermination is a particularly useful discriminant for such defectsbecause it is approximately proportional to the distance along the cablewhere the defect occurs. Thus, if interrogation of a particulartransducing element results in no capacitance, the respective cable maynot be connected with that transducing element. If interrogation of thattransducing element results in a capacitance that is half what isotherwise expected for a properly functioning transducing element, therespective cable may be broken or otherwise damaged approximatelyhalfway along the length of the cable.

3. Acoustic-System Testing

Embodiments of the invention may be used for testing the operation of avariety of different acoustic systems. These embodiments are illustratedwith a type of acoustic system shown schematically with the structuraldiagram of FIG. 9, although it will be evident to those of skill in theart after reading this description that the methods and apparatus of theinvention may alternatively be used for operational diagnosis of othertypes of acoustic systems. The components shown for the acoustic-systemstructure in FIG. 9 are shared by a large number of different acousticsystems, although specific systems may have these components organizeddifferently.

The acoustic system 900 includes a multichannel interface 902 that is incommunication with receiver 904 and transmitter 908 components. Thereceiver 904 and transmitter 908 are configured for conversion betweenelectrical and acoustic signals so that investigation of an object maybe performed by irradiating the object with the acoustic signals butperforming analysis with the electrical signals. Thus, the receiver 904may include components that convert acoustic signals to electricalsignals while the transmitter 908 may conversely include components thatconvert electrical signals to acoustic signals. Generally, each of thereceiver 904 and transmitter 908 are configured with multichannelcapacity. The receiver 904 may be provided in communication with anamplifier 912 and analog-to-digital converter 916 to accommodateacoustic signals that may be attenuated after scattering by the objectby amplifying and digitizing the converted electrical signals. Thus,after digitization, differences between the received and transmittedelectrical signals provide information derived from scattering of thecorresponding acoustic signals from the object.

The multichannel information provided from the multichannel interface902 is accommodated by a receive beamformer 920 and a transmitbeamformer 924, each of which is respectively configured for addingcontributions from a plurality of elements comprised by the receiver andtransmitter elements 904 and 908. The receive and transmit beamformers920 and 924 include array phasing capability to be applied respectivelyfor the received and transmitted signals. The acoustic system 900 mayinclude a capacity for displaying an image, which is typically viewed byan operator trained in evaluating acoustic images so that features ofinterest in the object, such as medical pathologies in an organ, may beidentified. The image is generated by a scan converter 932 provided incommunication with the receive and transmit beamformers 920 and 924 andtransmitted to a display 928 for rendering.

The testing methods and apparatus provided by embodiments of theinvention may be used to diagnose the operational behavior of acousticsystems such as that described in connection with FIG. 9. In particular,embodiments of the invention permit defects to be identified in theoperation of individual receiver and transmitter elements. Such defectsare often not immediately apparent in the image provided on the display928 because the image is derived from multiple elements. Nevertheless,the absence of information from a defective element may result in subtledistortions of the image that may lead to incorrect analyses of theobject under study. An overview of embodiments of the invention suitablefor testing the acoustic system 900 is provided with the structuraldiagram of FIG. 10. Similar to the apparatus used for acoustic-probetesting, the acoustic-system testing apparatus includes a relay matrix108′ adapted to perform signal mapping from one channel to a pluralityof channels in communication with an adapter 104′. For interrogation ofchannels within the system, a multichannel connection interface 1016 maybe provided between the adapter 104′ and the acoustic system 900.

In one embodiment, the natural cycling of the acoustic system 900through its multiple channels is used to evaluate operation oftransmitter elements. Signals generated by elements of the transmitter908 are collected by the adapter 104′ through the connection interface1016 and provided to the relay matrix 108′. The relay matrix 108′ isconfigured for discrimination of individual channels received from theadapter 104′ in the same manner described above for probe testing.Signal corresponding to the selected channels are provided to ananalog-to-digital converter 1032, perhaps after attenuation and/oramplification by an attenuator 1034 and/or amplifier 1028. The digitizedsignals are provided to a computational unit 136′, which thussystematically identifies whether a signal has been received from eachof the transmitter elements comprised by the acoustic system 900.

In another embodiment, operation of the receiver elements may beevaluated by providing synthesized echo information back into theacoustic system 900. In response to a transmit signal received by theadapter 104′ from the acoustic system 900 through the connectioninterface 1016, a trigger generator 1020 activates an echo synthesizer1024, which generates a signal to be routed back into the acousticsystem 900 for receipt by the receiver 904. Specific channelscorresponding to different elements comprised by the receiver 904 areselected according to a configuration of the relay matrix 108′ and theecho signal output from the relay matrix 108′ is transmitted with theadapter 104′ to the acoustic system 900. In this way, the echo signal isdirected to a specific element comprised by the receiver 904, causing adot to be displayed on the display 928 for each beam that that elementis used on. A defective channel may thus be characterized by the absenceof an expected line on the display. Such absence may be identified by ahuman operator, although in other embodiments a frame-capture device isinterfaced with the video output to detect the presence or absence oflines automatically. In an alternative embodiment, Doppler informationmay be analyzed to identify defective channels. The relay matrix 108′may be cycled through each of the channels corresponding to all elementscomprised by the receiver 904 to evaluate the operation of each of thoseelements. The components of the acoustic-system testing apparatus may becontrolled by a computational unit 136′ in a similar fashion to thecontrol provided for the acoustic-probe testing apparatus.

FIGS. 11A and 11B thus provide flow diagrams to summarize methods thatmay be used for testing an acoustic system in accordance withembodiments of the invention. FIG. 11A provides a flow diagram fortesting operation of a transmitter comprised by the acoustic system byusing the natural cycling of the acoustic system through differenttransmission channels. Thus, at block 1104, the acoustic systemactivates a first of a plurality of transmitter elements comprised bythe transmitter as part of such cycling. At block 1108, the transmissionsignal generated by the activated transmitter element is received. Acheck is made at block 1112 whether all of the transmitter elements havebeen activated, i.e. whether a full cycle of the acoustic system hasbeen completed. If not, the method waits for the acoustic system toactivate the next transmitter element at block 1116 so that thetransmission signal for that transmitter element may be received. Afterat least one full cycle has been completed, a comparison is performed ofthe amplitude of the different transmission signals. Absence of a signalor other significant deviation of the amplitude of the signal from theamplitude of the other signals is indicative of a defect associated withthe corresponding transmitter element.

FIG. 11B provides a flow diagram for testing operation of a receivercomprised by the acoustic system by using the echo-synthesis componentsdescribed above. In this instance, systematic interrogation of channelsin the acoustic system is coordinated externally. Thus, at block 1124,the first channel to be interrogated is selected. An echo signal isgenerated at block 1128 and transmitted to the acoustic system at block1132. Display data corresponding to the echo signal is captured at block1136, with the method looping as indicated at blocks 1140 and 1144 untilall channels have been interrogated. At block 1148, defective receiverelements are identified from image data generated by the acousticsystem, such as by identifying the presence or absence in the image dataof lines corresponding to specific receiver elements.

In some embodiments, a capacitance analysis may be added to the methodsdescribed above for testing an acoustic system. Such an analysis may beperformed in a manner similar to that described above for acoustic-probetesting by configuring a waveform generator to supply a waveform thatmay be used to determine the capacitance of the transmitter and/orreceiver elements. Knowledge of the capacitance may be used as describedabove to limit the type of defect identified more narrowly.

4. Adapter Configurations

There are a variety of different adapter configurations that may be usedin different embodiments of the invention, some of which are describedin detail herein. According to one embodiment, illustrated in FIG. 12,the adapter 104″ includes internal switching capability in the form ofan internal N-channel switch 1204. Inclusion of such capacity providesan economical way of increasing the channel capability of the testingapparatus.

Merely by way of example, consider the case where the testing apparatusis to be used to test a 192-channel probe or system. In such instances,interfacing the 192 channels through the adapter with the relay matrix108″ may be accomplished with, say, a 260-pin zero-insertion force(“ZIF”) connector 1208. Such connectors are readily availablecommercially at reasonable cost and have sufficient numbers of pins toaccommodate the 192 channels as well as power connections, groundconnections, computer connections, and the like. If the testingapparatus is then to be used to test a 256-channel probe or system, thecapacity of the connector 1208 is insufficient. Replacement of the260-pin ZIF connector with a larger connector greatly increases theoverall cost of the apparatus and makes inventory control difficultbecause such larger connectors are considerably more costly and havepoor distribution availability.

These disadvantages are avoided by including the N-channel switch 1204in the adapter. Referring again to the example above, a 256-channelprobe or system may be tested with the apparatus even with a 260-pin ZIFconnector 1208 since some of the mapping of channels may be performed bya 64-channel switch 1204. In the case of a probe test, the imposedinterrogation channel may be selected by a combination of routingthrough the relay matrix 108″ and the N-channel switch 1204. In the caseof a system test, use of the natural system cycling may similarly beaccommodated by a combination of routing through the relay matrix 108″and the N-channel switch 1204.

There are a variety of configurations that may be used to implement theN-channel switch 1204. For example, FIG. 13A illustrates an embodimentin which a plurality N of single-channel switches are used directly toimplement the N-channel switch 1304, with one terminal of each of thesingle-channel switches being connected together electrically. Inanother embodiment, illustrated in FIG. 13B, single-channel switches areelectrically connected in a tree arrangement to form the N-channelswitch 1308. The tree arrangement defines banks of single-channelswitches such that at any time no more that one bank is active. Forexample, banks may be provided that have only sixteen, eight, or someother appropriate number of single-channel switches. Although the totalnumber of single-channel switches in such an embodiment may be greaterthan N, this configuration limits the capacitance associated with theadapter 104, which might otherwise interfere with the capability of thetesting apparatus to make accurate measurements. The tree arrangement isthus particularly useful in embodiments where capacitance determinationsare used as part of the acoustic probe or system diagnosis.

FIG. 14 provides a flow diagram that summarizes how use of an adaptercomprising an N-channel switch may be integrated into a method fortesting an acoustic probe; it will be evident to those of skill in theart that it may similarly be integrated into a method for testing anacoustic system. In this embodiment, the adapter 104″ may substitute forthe adapter 104 in FIG. 1. At block 1404, a first channel is selectedfor interrogation. The electrical transmission signal to be used for theinterrogation is generated at block 1408. The electrical transmissionsignal is routed to the selected channel through a combination routingsthrough a relay matrix and a switch in the adapter respectively atblocks 1410 and 1412. A transducing element comprised by the acousticprobe that corresponds to the selected channel converts the electricaltransmission signal to an acoustic transmission signal at block 1416.After the acoustic transmission signal has been reflected from a targetat block 1420, it is received at block 1424 and converted to anelectrical received signal at block 1428. Data are collected in thismanner by interrogating all channels of the probe, as indicated with thelooping blocks 1432 and 1436, so that a comparison may be made of therelative amplitudes of the received signals at block 1440 to analyze theoperation of the probe as described above. The order of the blockspresented in FIG. 14 is intended to be exemplary and not limiting; otherorders for the functions described may alternatively be used withoutexceeding the intended scope of the invention. Furthermore, otherdiagnostic aspects may be incorporated into the method described withrespect to FIG. 14, such as the use of capacitance determinationsdescribed previously.

In another embodiment, an adapter may be provided for methods andapparatus used in testing a multiplexing acoustic probe. As used herein,a “multiplexing acoustic probe” refers to an acoustic probe that isequipped with internal switching capability to allow the probe itself tomap a greater number of transducing elements on the probe to a smallernumber of channels. Such a multiplexing capability permits the internalswitching capability to act as a surrogate for a larger number ofchannels that need be accommodated on a nonmultiplexing acoustic probewith the same element capacity. The structure of such a probe isillustrated schematically in FIG. 15, which shows more generally howembodiments of the invention may be used to test the operation of such aprobe.

The multiplexing acoustic probe 1504 includes a switch matrix 1508 thatperforms the mapping from the input channels onto the greater number oftransducing elements. In addition to an interface 1512 for communicatinginformation over the input channels between the switch matrix 1508 andan adapter 104′″, interfaces 1516 and 1520 may be included for providingswitch-selection information from the adapter 104′″ to the switch matrix1508 and for providing power from the adapter 104′″ to the switch matrix1508. As in other embodiments, the adapter 104′″ is provided incommunication with a relay matrix 108′″ configured to route signalsselectively to perform methods of the invention. While for convenienceonly the adapter 104′″ and relay matrix 108′″ are explicitly shown inFIG. 15, the apparatus may additionally include other componentsdescribed in connection with FIG. 1.

FIG. 16 provides a flow diagram illustrating a method for testing amultiplexing acoustic probe in accordance with an embodiment. At block1604, a first transducing element comprised by the multiplexing acousticprobe is selected for interrogation. The electrical transmission signalto be used for the interrogation is generated at block 1608, and isrouted to the selected transducing element. Such routing may beperformed in part by the relay matrix 108′″ and in part by the adapter104′″ if it is equipped with internal switching capability. In addition,the routing to the selected transducing element is performed at least inpart by the switch matrix 1508. This may include transmittingswitch-selection information to the switch matrix 1508 at block 1612,providing power to the switch matrix 1508 at block 1620, and thenrouting the electrical transmission signal through the switch matrix1508 at block 1624. The selected transducing element responds to theelectrical transmission signals by converting it to an acoustic signalat block 1628 that may be reflected from a target at block 1632. Afterreceiving the reflected acoustic signal at block 1636, it is convertedto an electrical received signal at block 1640. This technique is usedto collect data corresponding to all the transducing elements of themultiplexing acoustic probe, as indicated by blocks 1644 and 1648,allowing a comparison of relative amplitudes to be made at block 1652 toanalyze the functionality of the transducing elements. The functionsillustrated in FIG. 16 are not exhaustive, nor is the order in whichthey are presented necessary. For example, other diagnostic aspects maybe incorporated, such as the use of capacitance determinations describedpreviously, and the order of the functions may be changed withoutexceeding the intended scope of the invention.

It is evident that the methods and apparatus described above providespecific information regarding the characteristics and behavior ofindividual acoustic probes that may be collected by the computationalunit. This information may be used to define a probe-identificationcatalog so that automatic probe identification is performed when theapparatus is connected with the probe.

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. Accordingly, the above description should not be taken aslimiting the scope of the invention, which is defined in the followingclaims.

1. A method for testing an acoustic device having a plurality oftransducing elements adapted for conversion between acoustic andelectrical signals, the method comprising: generating an electricaltransmission signal; transmitting the electrical transmission signal toa selected transducing element; receiving an electrical received signalfrom the acoustic device; generating a reference signal with a frequencyless than 100 kHz; determining a capacitance associated with theselected transducing element from the reference signal; and diagnosingoperational characteristics of the selected transducing element from thedetermined capacitance and the electrical received signal.
 2. The methodrecited in claim 1 wherein the electrical received signal corresponds toan acoustic signal converted from the electrical transmission signal andreflected from a target.
 3. The method recited in claim 1 wherein theelectrical transmission signal comprises a voltage pulse.
 4. The methodrecited in claim 1 wherein transmitting the electrical transmissionsignal comprises routing the electrical transmission signal through arelay element configured for selective routing from a channel to aplurality of channels.
 5. The method recited in claim 4 whereintransmitting the electrical transmission signal further comprisesrouting the electrical transmission signal through an adapter having amultichannel switch.
 6. The method recited in claim 1 wherein thereference signal comprises a linear voltage ramp signal.
 7. The methodrecited in claim 1 wherein generating the reference signal comprisesgenerating the reference signal with a frequency less than 10 kHz. 8.The method recited in claim 1 wherein the selected transducing elementcomprises a plurality of selected transducing elements.
 9. A method fortesting an acoustic device having a plurality of transducing elementsadapted for conversion between acoustic and electrical signals, themethod comprising: generating an electrical transmission signal;transmitting the electrical transmission signal to a selectedtransducing element; receiving an electrical received signal from theacoustic device; generating a reference signal; determining acapacitance associated with the selected transducing element from thereference signal; and diagnosing operational characteristics of theselected transducing element from the determined capacitance and theelectrical received signal, wherein: the selected transducing elementcomprises a piezoelectric crystal; the resonant frequency of thepiezoelectric crystal is between 2 and 10 MHz; and generating thereference signal comprises generating the reference signal with afrequency between 0.5 and 1.5 MHz.
 10. The method recited in claim 9wherein the electrical received signal corresponds to an acoustic signalconverted from the electrical transmission signal and reflected from atarget.
 11. The method recited in claim 9 wherein the electricaltransmission signal comprises a voltage pulse.
 12. The method recited inclaim 9 wherein the reference signal comprises a linear voltage rampsignal.
 13. The method recited in claim 9 wherein the selectedtransducing element comprises a plurality of selected transducingelements.
 14. A method for testing an acoustic device having a pluralityof transducing elements adapted for conversion between acoustic andelectrical signals, the method comprising: generating an electricaltransmission signal; transmitting the electrical transmission signal toa selected transducing element; receiving an electrical received signalfrom the acoustic device; generating a reference signal; determining acapacitance associated with the selected transducing element from thereference signal; and diagnosing operational characteristics of theselected transducing element from the determined capacitance and theelectrical received signal, wherein: the selected transducing elementcomprises a cable connection, the capacitance deriving at least in partfrom a cable capacitance of the cable connection; and diagnosingoperational characteristics comprises determining that the capacitancearising from the cable capacitance is a fraction of an expected value.15. The method recited in claim 14 wherein the electrical receivedsignal corresponds to an acoustic signal converted from the electricaltransmission signal and reflected from a target.
 16. The method recitedin claim 14 wherein the electrical transmission signal comprises avoltage pulse.
 17. The method recited in claim 14 wherein the referencesignal comprises a linear voltage ramp signal.
 18. The method recited inclaim 14 wherein the selected transducing element comprises a pluralityof selected transducing elements.
 19. A method for testing an acousticdevice having a plurality of transducing elements adapted for conversionbetween acoustic and electrical signals, the method comprising:generating an electrical transmission signal; transmitting theelectrical transmission signal to a selected transducing element;receiving an electrical received signal from the acoustic device;generating a reference signal; determining a capacitance associated withthe selected transducing element from the reference signal; anddiagnosing operational characteristics of the selected transducingelement from the determined capacitance and the electrical receivedsignal, wherein diagnosing the operational characteristics comprises:determining that an amplitude of the electrical received signal issubstantially zero; and determining whether the capacitance isconsistent with an expected value.
 20. The method recited in claim 19wherein the electrical received signal corresponds to an acoustic signalconverted from the electrical transmission signal and reflected from atarget.
 21. The method recited in claim 19 wherein the electricaltransmission signal comprises a voltage pulse.
 22. The method recited inclaim 19 wherein the reference signal comprises a linear voltage rampsignal.
 23. The method recited in claim 19 wherein the selectedtransducing element comprises a plurality of selected transducingelements.